This invention relates to image inspection systems, and more particularly to such systems which are especially suited to high speed inspection of repetitively occurring images and in which it is important to monitor the full grey scale integrity of the images.
Modern high speed printing and/or other product production equipment is capable of producing products at very high speeds. As just one example, cigarette pack blanks may be printed on continuous web presses at speeds of the order of 1000 feet per minute. Because each pack blank is approximately six inches long parallel to the length of the web, each line of pack blanks is coming off the press at the rate of approximately 2000 blanks per minute. (Several parallel lines of blanks (e.g., eight or nine) may be printed across the web.) Accordingly, if each pack blank in a line is treated as an image, the press is producing on the order of 2000 images per minute in each line. Despite the high speed at which such images are being produced, it would be highly desirable to be able to effect complete inspection of all the images. This preferably means inspecting all parts of all of the images, including the full grey scale information for as much of the images as is possible. (As used herein, grey scale means that each pixel in a digitized image is represented by a multidigit binary value or the equivalent thereof.)
Inspection systems are known which inspect only selected portions of images, and/or which discard much of the grey scale information in the images in order to reduce the computational burden. However, systems which inspect only parts of the images miss defects occurring elsewhere in the images. Furthermore, systems which discard available grey scale information may not be able to detect with sufficient promptness gradual fading and/or discoloration of the images.
Another disadvantage of the known systems which inspect only portions of the images and/or which make use of only portions of the information coming from the images is that these known systems tend to require set-up by relatively highly skilled operators who must devote substantial amounts of time to the set-up task. For example, if less than all of each image is to be inspected, the operator must make informed judgments as to the portions of the image which it is most important to inspect, as well as what the criteria for acceptance or rejection in each area will be. Moreover, this complex set-up task must be repeated each time different images are to be inspected.
In view of the foregoing, it is an object of this invention to provide image inspection systems which are capable of substantially complete inspection of images produced at very high speeds.
It is a more particular object of this invention to provide high speed image inspection systems which are capable of full grey scale inspection of at least portions of the images being inspected.
It is still another object of this invention to provide high speed image inspection systems which require relatively little operator time and skill to set them up for an image inspection procedure.